Hello thanks for the reply.
I have modified my code like this:

my $targetserver = 'files.responsys.net';
my $sftp = Net::SFTP->new(
    $targetserver,
    user     => 'canneu_scp',
    ssh_args => {
        identity_files => [ '/tmp/responsys/capgemini.private' ],
        debug => 1,
    }
) or die "could not open connection to $targetserver\n";
[download]

Now when I run this, I am getting the following error:

can-ornstein:[/tmp/responsys] ./testftp.pl
can-ornstein: Reading configuration data /home/home2/cgmjoshi/.ssh/con
+fig
can-ornstein: Reading configuration data /etc/ssh_config
can-ornstein: Connecting to files.responsys.net, port 22.
can-ornstein: Remote protocol version 2.0, remote software version Ope
+nSSH_5.2
can-ornstein: Net::SSH::Perl Version 1.34, protocol version 2.0.
.an-ornstein: No compat match: OpenSSH_5.2
can-ornstein: Connection established.
can-ornstein: Sent key-exchange init (KEXINIT), wait response.
can-ornstein: Algorithms, c->s: 3des-cbc hmac-sha1 none
can-ornstein: Algorithms, s->c: 3des-cbc hmac-sha1 none
can-ornstein: Entering Diffie-Hellman Group 1 key exchange.
can-ornstein: Sent DH public key, waiting for reply.
Key class 'Net::SSH::Perl::Key::DSA' is unsupported: Math::BigInt vers
+ion 1.78 required--this is only version 1.70 at /usr/lib/perl5/vendor
+_perl/5.8.5/Crypt/DSA/KeyChain.pm line 4, <GEN0> line 1.
BEGIN failed--compilation aborted at /usr/lib/perl5/vendor_perl/5.8.5/
+Crypt/DSA/KeyChain.pm line 4, <GEN0> line 1.
Compilation failed in require at /usr/lib/perl5/vendor_perl/5.8.5/Cryp
+t/DSA.pm line 7, <GEN0> line 1.
BEGIN failed--compilation aborted at /usr/lib/perl5/vendor_perl/5.8.5/
+Crypt/DSA.pm line 7, <GEN0> line 1.
Compilation failed in require at /usr/lib/perl5/vendor_perl/5.8.5/Net/
+SSH/Perl/Key/DSA.pm line 14, <GEN0> line 1.
BEGIN failed--compilation aborted at /usr/lib/perl5/vendor_perl/5.8.5/
+Net/SSH/Perl/Key/DSA.pm line 14, <GEN0> line 1.
Compilation failed in require at (eval 23) line 1, <GEN0> line 1.
BEGIN failed--compilation aborted at (eval 23) line 1, <GEN0> line 1.
[download]

The versions I am using are:

perl-Net-SFTP-0.10-1.el4.rf
perl-Net-SSH-Perl-1.34-1.el4.rf
perl-Math-Pari-2.01080603-1.el4.rf
perl-Math-GMP-2.05-1.el4.rf
[download]

Can anyone help how to get rid of this error?